Photofinishers that use photosensitive paper to produce color prints desire short processing times in order to increase output. One way of obtaining rapid processing is to accelerate the development time by increasing the chloride content of the emulsions used in the photographic paper. However, as the chloride content of a photographic emulsion is increased, it becomes more difficult to obtain good invariant photosensitivity.
One of the problems with silver chloride emulsions is their severe propensity to storage deterioration. Photographic emulsions that have a high silver chloride content are prone to fog increase due to high temperature and humidity during storage. These changes may vary from layer to layer resulting in color imbalance and a loss of quality of the print material. Attempts have been made to reduce fog formation during storage by addition of inhibitory agents to the silver halide emulsions. For example, U.S. Pat. Nos. T866,036; 2,440,110; 3,043,696; 3,057,725; 3,226,232; 3,397,986; 3,447,925; and 3,761,277 describe the addition of organic disulfides to silver halide emulsions to lessen the tendency towards fog growth.
High chloride content color print paper also has an undesirable sensitivity to temperature changes during exposure. For example, when the temperature upon exposure rises due to heat from the exposing element during printing, the print density changes if the printing conditions are left at the initial set values. This may result in prints varying in density that were exposed at the normal temperature. This density difference contributes to print variability and is not acceptable to photofinishers. Very often, an increase in temperature during exposure of the paper may result in a selective increase in speed in one layer, for instance the cyan layer, over another light sensitive layer such as the magenta layer. This results in improper color balance of the color print, and requires the photofinisher to readjust his printing conditions in order to compensate for this density fluctuation. This results in a loss in operating efficiency.
This deficiency in the use of high silver chloride color paper material is recognized in the art. In particular, EP 0 367,227 (1988) discusses reducing heat sensitivity by employing certain spectral sensitizing dyes in combination with mercapto azoles. However, these dye structures have not proved to be entirely satisfactory in terms of minimizing thermal sensitivity while still maintaining optimal sensitization efficiency. EP 0 325,235 describes using iron ion donating compounds in high chloride photographic elements to reduce their change in sensitivity due to exposure at elevated temperature. Despite these attempts to address the thermal problem, no solution has been found which completely eliminates the above concerns.
Phosphines are trivalent phosphorous compounds which have been described for use in silver halide emulsions. U.S. Pat. No. 4,515,888 describes using triphenyl phosphines and certain amidinium cyanine dyes to supersensitize an infrared sensitive silver halide emulsion. U.S. Pat. No. 4,578,347 describes a supersensitizing effect obtained from the use of water soluble triaryl phosphines in infrared sensitive silver halide emulsions. U.S. Pat. No. 4,346,154 describes using triaryl phosphines in an undercoat layer to retard stain formed from a post-process buildup of silver sulfide. U.S. Pat. No. 3,297,446 describes using a selenium sensitizer in an emulsion that also contains an antifogging amount of a tertiary phosphine antifoggant. U.S. Pat. No. 4,357,280 describes using water soluble phosphines to accelerate the bleaching of dye and silver in processing baths. Certain tris(dialkylamino)phosphines are described in U.S. Pat. No. 3,904,415 as having a sensitizing effect in silver bromide or silver bromoiodide emulsions. Russian Patent 195,872 discloses triphenyl phosphines to be useful sensitizers in silver halide emulsions. GB 1,295,463 teaches that silver halide emulsions can be sensitized through the use of gelatin which has been treated with phosphine. GB 1,066,261 teaches using phosphino aryl sulfonic acid salts as antifoggants in silver halide emulsions. None of these references describes using phosphine compounds to stabilize a photographic element against thermal changes during exposure.
Compounds with labile sulfur moieties have been extensively used as sensitizers of silver halide emulsions. Their use and mechanism of action have been discussed in the photographic art such as by Pouradier, J. Properties of Gelatin in Relation to Its Use in the Preparation of Photographic Emulsions; James, T. H. Ed.; The Theory of the Photographic Process, 4th ed.; Macmillan: New York, 1977, Chapter 2; by Duffin, G. F. Photographic Emulsion Chemistry; Focal: London, 1966, Chapter 2 and by Mueller, F. W. H. in The Photographic Emulsion, Sturge, J. M. Ed.; Neblette's Handbook of Photographic and Reprography, 7th ed.; Van Nostrand Reinhold: New York, 1977, Chapter 2. Common among these labile sulfur compounds are thionates, thioureas, thiosulfates, isothiocyanates and sulfur containing amino acids such as cystine.
Elemental sulfur (also known as inorganic sulfur) has been claimed to be useful in silver halide photographic emulsions. EP 0 447,105; EP 0 297,804; EP 0 294,149 (AgCl); EP 0 327,272; EP 0 349,286; JP 2,161,423; JP 2,148,033; JP 2,148,031; JP 2,146,036; JP 0 2,033,141; JP 2,020,857; JP 2,301,744; JP 1,196,050; JP 1,196,034; DE 3,902,711; and U.S. Pat. No. 4,962,016, describe the use of elemental sulfur for sensitizing silver halide emulsions.
Thiatriazoles have been used as supersensitizers for silver halide photographic materials as described in U.S. Pat. No. 4,914,015 (substituted thia and oxa thiatriazoles in red and infrared spectrally sensitized emulsions); U.S. Pat. No. 4,780,404 (amino thiatriazoles); EP 0 447,647 (arylaminothiatriazoles substituted with at least one electron-withdrawing group); and JP 3,033,842 and JP 3,041,438, (thiatriazoles as supersensitizers in red sensitized silver halide emulsions). JP 63/037,348 describes using thiatriazoles in silver chloride emulsions to obtain a low D-min photographic material. JP 63/044,650 and JP 63/037,349 describe a high storage stability material. U.S. Pat. No. 5,070,008 describes using thiatriazoles in silver chloride emulsions with iridium and acidic conditions for formation of AgCl grains. JP 80/142,331 describes using a thiatriazole in a photothermographic paper to reduce fog. U.S. Pat. No. 5,006,448 describes using a thiatriazole as an inhibitor fragment that is released for improving interimage effects.
Pyrazolopentathiepins have been described as fungicides or as sulfur sensitizers in photographic emulsions in EP 0 138,622. In JP 62/299,963 thiepin is mentioned as an example of a class of compounds used for the preparation of silver halide emulsions which comprises at least 50 mol % of silver bromide.
U.S. Pat. No. 4,960,689 describes using thiosulfonates in the finish in high Cl emulsions. Aromatic dithiosulfonic acids are described in U.S. Pat. No. 5,009,992 as supersensitizers in an IR-sensitive high Cl emulsion. WO 92/12,462 describes using thiosulfonates and sulfinates in controlling speed increase on incubation of color photographic materials. The combination of thiosulfonates with sulfinates has been used in the sensitization of chloride emulsions for color paper in JP 3,208,041. U.S. Pat. No. 2,394,198 discloses the use of sulfinates with thiosulfonates in stabilizing silver halide emulsions.
U.S. Pat. No. 2,385,762 describes using diamino disulfides and sufinates to stabilize silver halide emulsions. U.S. patent application Ser. No. 07/890,884 describes using diamino disulfides and sulfinates to reduce the thermal sensitivity of high chloride emulsions.
There remains a continuing need for an effective means for heat stabilizing high chloride emulsions against thermal changes.